Many forms of respirator apparatus of this type have been proposed and marketed but certain of these are of such a construction that the amount of head protection is less than that which can be provided with a conventional and non-respirated hard hat, and the level of respiratory protection provided in some of these devices is also limited to the lower order of respiratory hazards. There are statutory health and safety regulations in some countries that identify and set standards for protective helmets and respiratory devices. Some examples of these known devices are disclosed in patent specifications--Howie GB 2,201,601,A--Scott GB 2,227,158 and Berg/Kvaal PCT/US81/00244--Vaughan/Wiggins PCT/US82/01154--Gorman U.S. Pat. No. 4,136,688--Schoelz/Tidland U.S. Pat. No. 3,649,946, Chien U.S. Pat. No. 4,549,541--Depping U.S. Pat. No. 3,413,972--Guy U.S. Pat. No. 3,822,698--Grenough G.B. Patent No. 1,426,432, U.K. Patent 1,426,432,--1,495,020--European Patent 0047296, U.S. Pat. Nos. 3,258,010--3,649,964 and 3,822,698.
Examples of devices presently manufactured are the Airstream and Jupiter helmets manufactured by Racal Ltd.; The PF2 and PF3 Helmets manufactured by Pureflo Ltd., and the Clearflow Turbovisor manufactured by Pulsafe Ltd. All of these devices have features that make them difficult, awkward or cumbersome to use.